I don't recall which book the comment may have come from... However the efficiency standard for a typical Infantryman is trained to at least be able to fire three rounds in a minute... Four is seriously pushing it... especially for a muzzle loader....

In Deer hunting... you do typically only have chance for the single shot... If you miss... the blast and noise.. the target usually dashes out of range or out of view before you can tear open the next cartridge... As compared to a target that could be still standing there shooting back or charging at you.....